Method for fabricating tandem thin film photoelectric converter

ABSTRACT

A method of manufacturing a tandem-type thin film photoelectric conversion device includes the steps of forming at least one photoelectric conversion unit ( 3 ) on a substrate ( 1 ) in a deposition apparatus, taking out the substrate ( 1 ) having the photoelectric conversion unit ( 3 ) from the deposition apparatus to the air, introducing the substrate ( 1 ) into a deposition apparatus and carrying out plasma exposure processing on the substrate ( 1 ) in an atmosphere of a gas mixture containing an impurity for determining the conductivity type of the same conductivity type as that of the uppermost conductivity type layer ( 33 ) and hydrogen, forming a conductivity type intermediate layer ( 5 ) by additionally supplying semiconductor raw gas to the deposition apparatus, and then forming a subsequent photoelectric conversion unit ( 4 ).

TECHNICAL FIELD

The present invention relates to a method of manufacturing a tandem-typethin film photoelectric conversion device and, more particularly, to amethod of manufacturing which can suppress reduction in performance of aphotoelectric conversion device, enhance the flexibility ofmanufacturing steps and improve manufacturing efficiency. In thespecification, terms “crystalline” and “microcrystalline” are used alsofor a state partially including amorphous regions, as generally used inthe field of the art.

BACKGROUND ART

In recent years, semiconductor thin film photoelectric conversiondevices as represented by a solar cell have been diversified, andcrystalline silicon thin film solar cells have been developed inaddition to conventional amorphous silicon thin film solar cells.Furthermore, a tandem (hybrid)-type thin film solar cell having a stackthereof have come into practical use.

In general, a silicon thin film photoelectric conversion device includesa first electrode, one or more semiconductor thin film photoelectricconversion units and a second electrode stacked in sequence on asubstrate at least a surface portion of which is insulated. Further, onephotoelectric conversion unit includes an i-type layer sandwichedbetween a p-type layer and an n-type layer.

A major portion of the thickness of the thin film photoelectricconversion unit is occupied by the i-type layer of a substantiallyintrinsic semiconductor layer and photoelectric conversion occurs mainlyin the i-type layer. Accordingly, it is preferable that the i-type layeras a photoelectric conversion layer has a greater thickness for thepurpose of light absorption, though increase of the thickness increasescosts and time for deposition of the i-type layer.

The p-type and n-type conductive layers serve to produce a diffusionpotential within the photoelectric conversion unit, and magnitude of thediffusion potential affects the value of open-circuit voltage which isone of important properties of the thin film photoelectric conversiondevice. However, these conductive layers are inactive layers which donot directly contribute to photoelectric conversion. That is, lightabsorbed by these inactive layers is a loss, which does not contributeto electric power generation. Consequently, it is preferable to minimizethe thickness of the p-type and n-type conductive layers as far as theyprovide a sufficient diffusion potential.

For this reason, regardless of whether p-type and n-type conductivitytype layers included in a photoelectric conversion unit or aphotoelectric conversion device is amorphous or crystalline, one whosei-type photoelectric conversion layer which occupies a major portion ofthe conductivity type layer is amorphous is called an amorphous unit oran amorphous photoelectric conversion device, and one whose i-type layeris crystalline is called a crystalline unit or a crystallinephotoelectric conversion device.

Currently, a wide variety of materials and forming technologies havebeen developed for achieving quality required for conductivity typelayers included in a photoelectric conversion device. As a material fora conductivity type layer of a silicon photoelectric conversion device,amorphous silicon or its alloy material or crystalline silicon or itsalloy material is generally used. Generally, an amorphous siliconmaterial having a wider band gap than that of a photoelectric conversionlayer (i-type layer) or a microcrystalline silicon material having ahigh impurity activation rate is used for a conductivity type layer,with the intention to attain a high photoelectric conversioncharacteristic while reducing electric and optical losses as small aspossible.

A conductive layer of a silicon photoelectric conversion unit isgenerally formed by a method substantially the same as that for aphotoelectric conversion layer (i-type layer) such as a plasma CVDmethod. The conductive layer is formed from reaction gas which is amixture of a raw gas containing atoms of silicon and doping gascontaining atoms of a conductivity-type determining impurity. In recentyears, a modified process of general plasma CVD method has beenattempted in order to form the conductivity type layer.

For example, JP-A-06-232429 discloses a plasma doping method in which ani-type layer is once formed by a plasma CVD method and then plasmaprocessing is carried out in an atmosphere containing a mixture ofdoping gas and a dilution gas such as hydrogen whereby an area near asurface of the i-type layer is changed to a conductivity type layer.Alternatively, JP-A-10-074969 discloses a method for improvingcrystallinity of a conductivity type layer in which a conductivity typemicrocrystalline layer is once formed by a plasma CVD method and thenplasma processing is carried out in a hydrogen atmosphere. In both ofthe methods, film deposition by the plasma CVD method and subsequentplasma processing are carried out as continuous processes in adecompression reaction chamber. Thus, a good junction interface and ahigh quality conductivity type layer can be formed.

In order to enhance a conversion efficiency of a thin film photoelectricconversion device, it is known that two or more photoelectric conversionunits are stacked to form a tandem-type thin film photoelectricconversion device. In this case, a front unit including a photoelectricconversion layer having a large band gap (such as of an amorphoussilicon or an Si—C alloy) is disposed closer to the light incident sideof the photoelectric conversion device, and a rear unit including aphotoelectric conversion layer having a small band gap (such as of anSi—Ge alloy) is disposed behind the front unit in sequence. Thus,photoelectric conversion can be performed over a wide wavelength rangeof incident light, and the conversion efficiency of the entirephotoelectric conversion device can be improved. Among such tandem-typethin film photoelectric conversion devices, one including both of anamorphous photoelectric conversion unit and a crystalline photoelectricconversion unit is occasionally called a hybrid thin film solar cell inparticular.

For example, a wavelength of light that can be photoelectricallyconverted by an i-type amorphous silicon ranges to about 800 nm maximumon the long wavelength side, while an i-type crystalline silicon canphotoelectrically convert light having a longer wavelength ranging toabout 1100 nm. Here, an amorphous silicon photoelectric conversion layerhaving large light absorption is enough to light absorption in thethickness of about 0.3 μm or less even in the case of a single layer.However, in order to sufficiently absorb light of a longer wavelengthalso, a crystalline silicon photoelectric conversion layer having asmall light absorption coefficient is preferably about 2 to 3 μm thickor above in the case of a single layer. In other words, a crystallinephotoelectric conversion layer generally desirably has a large thicknessabout ten times of that of an amorphous photoelectric conversion layer.

In the tandem-type thin film photoelectric conversion device, respectivephotoelectric conversion units are desired to be formed under respectiveoptimum conditions. Therefore, the respective photoelectric conversionunits may be formed discontinuously by separate deposition apparatuses.Furthermore, in order to enhance flexibility of manufacturing processesof the tandem-type thin film photoelectric conversion device and toimprove production efficiency, the respective photoelectric conversionunits may be desired to be formed discontinuously by separate depositionapparatuses.

However, the inventors experienced that, when a first photoelectricconversion unit was formed, then a substrate including the unit was oncetaken out to the air from a deposition apparatus, and a secondphotoelectric unit was stacked thereafter, characteristics of theresulting tandem-type thin film photoelectric conversion devicedeteriorate as compared to that of a tandem-type thin film photoelectricconversion device wherein all units were continuously formed withouttaking a substrate out to the air.

DISCLOSURE OF THE INVENTION

In view of the circumstances of the conventional arts, the invention isaimed at to minimize the reduction in photoelectric conversionefficiency of a tandem-type thin film photoelectric conversion devicedue to exposure to the air when a substrate having one or morephotoelectric conversion units is once taken out to the air from adeposition apparatus in mid-course of formation of a plurality of theunits involved in the photoelectric conversion unit.

A method of manufacturing a tandem-type thin film photoelectricconversion device according to the invention includes the steps offorming at least one photoelectric conversion unit on a substrate in adeposition apparatus, taking out the substrate having the photoelectricconversion unit to the air from the deposition apparatus, introducingthe substrate into a deposition apparatus and carrying out plasmaexposure processing on the substrate in an atmosphere of a gas mixturecontaining an impurity element for determining the conductivity type ofthe same type as that of the uppermost conductivity type layer of thephotoelectric conversion unit on the substrate and hydrogen, forming aconductivity type intermediate layer by additionally supplying asemiconductor raw gas to the deposition apparatus, and then forming asubsequent photoelectric conversion unit.

In any photoelectric conversion unit included in the tandem-type thinfilm photoelectric conversion device, a one-conductivity type layer, aphotoelectric conversion layer of substantially intrinsic semiconductorand an opposite-conductivity type layer are stacked in sequence. Thetandem-type thin film photoelectric conversion device preferablyincludes at least one amorphous silicon thin film photoelectricconversion unit and at least one crystalline silicon thin filmphotoelectric conversion unit.

Preferably, a non-doped intermediate layer having a thickness of 5 nm orless is formed subsequently to the formation of the at least onephotoelectric conversion unit on the substrate and the substrate is thentaking out to the air.

The plasma exposure processing is preferably carried out for 60 secondsor less using high frequency discharging at a frequency of 13.56 MHz orhigher in the mixed atmosphere containing the gas containing the elementfor determining the conductivity-type in an amount of 20 ppm or morebased on the hydrogen. The plasma exposure processing and the formationof the conductivity-type intermediate layer are preferably carried outin the same deposition apparatus and under substantially the samepressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section diagram showing a tandem-type thinfilm photoelectric conversion device manufactured by a method ofmanufacturing according to an embodiment of the invention.

FIG. 2 is a schematic cross section diagram showing a tandem-type thinfilm photoelectric conversion device manufactured by a method ofmanufacturing according to another embodiment of the invention.

FIG. 3 is a transmission electron microscopic (TEM) photograph showing across section structure in the vicinity of a boundary between anamorphous unit and a crystalline unit in a hybrid-type thin filmphotoelectric conversion device according to Example 1 of the invention.

FIG. 4 is a TEM photograph showing a cross section structure in thevicinity of a boundary between an amorphous unit and a crystalline unitin a hybrid-type thin film photoelectric conversion device according toReference Example.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the invention will be described below withreference to the drawings. In order to clarify and simplify thedrawings, dimension relationships of the thickness, the length and thelike are modified appropriately in the drawings of this application, andthey do not show the actual dimension relationships. In the drawings,the same reference numerals are given to the same components andequivalent parts in the drawings.

FIG. 1 shows a schematic cross section diagram of a silicon tandem-typethin film photoelectric conversion device manufactured by a methodaccording to an embodiment of the invention. Namely, in thephotoelectric conversion device, a transparent electrode 2 made of atransparent conductive oxide (TCO) film is formed on a transparentinsulative substrate 1 made of glass or the like. On the transparentelectrode 2, a one-conductivity type layer 31, a intrinsic semiconductoramorphous or crystalline photoelectric conversion layer 32 and anopposite-conductivity type layer 33 included in a first photoelectricconversion unit 3 are deposited in sequence preferably by plasma CVD (orthey may be deposited by other chemical vapor deposition as a matter ofcourse). Preferably, a P-type layer 31, a substantially intrinsicsemiconductor photoelectric conversion layer 32 and an n-type layer 33are deposited in this order.

After the first photoelectric conversion unit 3 is formed, the substrate1 is taken out from a plasma CVD apparatus to the air whereby, thesurface of the opposite-conductivity type layer 33 is exposed to theair. Then, the substrate 1 is introduced into another plasma CVDapparatus and undergoes plasma exposure processing in a mixed atmosphereof doping gas containing an element for determining the conductivitytype of the same type as that of the opposite-conductivity type layer 33(such as phosphine) and hydrogen. As the doping gas, gas containingphosphorus, oxygen and the like may be used for n-type and, inparticular, phosphorus is preferably contained. In the case of p-type,doping gas containing boron, aluminum and the like may be used and, inparticular, boron (such as diborane) is preferably contained.

Next, an intermediate layer 5 of the same opposite conductivity type asthat of the plasma-exposed opposite-conductivity-type layer 33 is formedthereon. More specifically, when the opposite conductivity type layer 33is of n-type, the intermediate layer 5 is also made to be n-type, andwhen the opposite conductivity type layer 33 is of p-type, theintermediate layer 5 is also made to be p-type. The conductivity typeintermediate layer 5 is preferably a fresh additional layer, which canact such that a good np (or pn) tunnel junction is formed between theintermediate layer 5 and a subsequent photoelectric conversion unit 4.The opposite conductivity type intermediate layer 5 is preferablydeposited by plasma CVD.

The conductivity type intermediate layer 5 may be formed by adjustingdeposition gas containing a new doping element after plasma exposureprocessing. However, the conductive intermediate layer 5 can be formedsimply by performing plasma exposure processing with doping gas andhydrogen and then additionally supplying semiconductor raw gas to areaction chamber. Here, the semiconductor raw gas may be silane forsilicon, silane and methane for silicon carbide or silane and germanefor a silicon-germanium alloy.

A one-conductivity type layer 41, a substantially intrinsicsemiconductor amorphous or crystalline photoelectric conversion layer 42and an opposite conductivity type layer 43 included in a secondphotoelectric conversion unit 4 are deposited in sequence on theopposite conductivity type intermediate layer 5 preferably by plasmaCVD. Finally, a back electrode 10 is formed thereon.

The plasma exposure processing, the formation of the oppositeconductivity type intermediate layer 5 and the formation of the oneconductivity-type layer 41 in the second photoelectric conversion unit 4are preferably carried out in the same decompression reaction chamberand are preferably carried out under substantially the same pressure.After the completion of the plasma exposure processing, the intermediatelayer 5 can be formed continuously by additionally supplying thesemiconductor raw gas such as silane to the reaction chamber immediatelywithout stopping plasma discharging resulting from the application ofhigh frequency electric power. In some cases, the one-conductivity typelayer 41 can be further formed. In such a method, though the steps ofplasma exposure processing and formation of the intermediate layer 5 areadded, the addition of time and facility required for these steps can bekept at minimum.

With the method of manufacturing a tandem-type thin film photoelectricconversion device, even when the surface of theopposite-conductivity-type layer 33 of the first photoelectricconversion unit 3 is deteriorated due to the air-exposure, the surfacecan be cleaned or reformed by plasma exposure processing. Here, asimilar effect can be expected from plasma exposure processing only in ahydrogen atmosphere without doping gas. However, plasma exposureprocessing with hydrogen only may adversely affect the quality of asilicon film in the vicinity of the surface to be processed. Therefore,it is believed that plasma exposure processing is preferably carried outwith mixed gas of doping gas and hydrogen.

In fact, when plasma exposure processing was carried out with hydrogenonly, the photoelectric conversion characteristic was slightly lowerthan that of the case where the first and second units 3 and 4 areformed continuously without exposure to the air. Furthermore, thereproducibility was not very high. On the other hand, when plasmaprocessing was carried out in an atmosphere of hydrogen mixed withdoping gas like the invention, almost the same photoelectric conversioncharacteristic was obtained as that of the continuous formation withoutexposure to the air.

The reason why these effects are brought about is considered that theplasma exposure with hydrogen only results in increase in resistance dueto a phenomenon that a part of impurity atoms in the conductivity typelayer 33 in the vicinity of the air-exposed surface is inactivated orleaves from the layer. On the other hand, it is considered that, whenplasma processing is carried out with doping gas being mixed, suchincrease in resistance can be prevented, whereby the conductivity of theconductivity type layer 33 can be maintained. Alternatively, it is alsoconsidered that mixing of doping gas can reduce the increase inresistance because of decrease in carrier mobility of the conductivitytype layer 33 due to the occurrence of defects or irregularity in thefilm structure resulting from a plasma damage, which is often a problemin hydrogen plasma processing.

The hydrogen plasma processing with doping gas being mixed is carriedout preferably within two minutes, more preferably within one minute,through high-frequency discharging at a frequency equal to or higherthan 13.56 MHz. Discharging at a lower frequency than the frequency or alonger processing time than the time may increase a side effect such asa plasma damage near the surface to be processed.

Since an increase in costs of a high frequency power supply can beprevented by setting a discharging frequency in the plasma processing tobe the same as the frequency employed in the subsequent forming stepsfor semiconductor layers, a frequency equal to or higher than 13.56 MHzis preferably used. This is because the fact that plasma discharging atsuch a high frequency is preferably used for forming a high performancethin film photoelectric conversion unit is widely recognized inexperimental and industrial points of view. In view of a productivity,the plasma processing time is preferably as short as possible. In orderto make certain of the effect of addition of the doping gas, theconcentration of the doping gas is preferably 20 ppm or more based onhydrogen.

When it becomes possible to form a plurality of photoelectric conversionunits in separate plasma CVD apparatuses in this way, optimum facilityspecifications and forming conditions for achieving best characteristicsrequired for the respective units can be set independently. Thus,improvement in the characteristic of the tandem-type thin filmphotoelectric conversion apparatus as a whole can be expected.Furthermore, since a plurality of production lines can be used for therespective units, the production efficiency and the flexibility forchanges and additions of the lines can be increased. Still further, as aplurality of manufacturing apparatuses are used, maintenance thereof canbe carried out one by one smoothly.

FIG. 2 shows a schematic cross section diagram of a tandem-type thinfilm photoelectric conversion device manufactured by a method ofmanufacturing according to another embodiment of the invention. Theapparatus in FIG. 2 is similar to that of FIG. 1 but differs in that anadditional non-doped intermediate layer 6 is formed subsequent to thedeposition of the opposite conductivity type layer 33 included in thefirst photoelectric conversion unit 3. The non-doped intermediate layer6 is preferably in the thickness of 5 nm or less, which may cause atunnel effect. The non-doped intermediate layer 6 may be producedpreferably by plasma CVD but may be produced by other different kinds offormation methods.

After the non-doped intermediate layer 6 is formed, the substrate 1 istaken out from the plasma CVD apparatus to the air, and the outermostsurface of the non-doped intermediate layer is exposed to the air.According to the review by the inventors, the surface tends to be porouswhen impurity atoms (such as phosphorus for an n-type layer, especially)are doped therein like a conductivity-type layer. As the dopingconcentration increases, the tendency increases. Therefore, the exposureof the porous surface of the conductivity-type layer 33 according to theembodiment in FIG. 1 into the air may likely accelerate the oxidizationof and/or the adhesion of a foreign substance to the porous surface ascompared to the case of a flat surface.

On the other hand, as compared to the conductivity-type layer, thesurface of the non-doped intermediate layer 6 may not likely bedeteriorated or contaminated when the non-doped intermediate layer isexposed to the air. The non-doped intermediate layer 6 does not inhibitcurrent flow because it causes a tunnel effect when its thickness is 5nm or less, therefore, the non-doped intermediate layer 6 is less apt tobe a factor that causes decrease in the electric characteristic as anphotoelectric conversion device.

After the surface of the non-doped intermediate layer 6 is exposed tothe air, hydrogen plasma exposure processing with doping gas being mixedis carried out on the non-doped intermediate layer 6 also in the case inFIG. 2 like the case in FIG. 1. Subsequently, the opposite-conductivitytype intermediate layer 5 and the second photoelectric conversion unit 4are formed by plasma CVD.

The opposite-conductivity type intermediate layer 5 is formed in both ofthe embodiments in FIGS. 1 and 2. Since the opposite-conductivity typeintermediate layer 5 can also act to support the function of theopposite-conductivity type layer 33 of the first photoelectricconversion unit 3, the opposite conductivity type intermediate layer 5may be considered as a part of the opposite conductivity type layer 33.Since the one-conductivity type layer 41 of the second photoelectricconversion unit 4 is formed continuously on the opposite conductivitytype intermediate layer 5 without exposing the opposite conductivitytype intermediate layer 5 to the air, it is expected that a good np (orpn) tunnel junction, which is desirable for achieving a highphotoelectric conversion characteristic in the tandem-type photoelectricconversion device, is formed.

The photoelectric conversion devices according to these embodiments mayhave a so-called super-straight structure having the back electrode 10on the two photoelectric conversion units 3 and 4 includingsemiconductor layers in the pin order stacked on the glass substrate 1.Alternatively, the photoelectric conversion devices may have a so-calledsub-straight structure having the transparent electrode 10 on a multipleof the units 3 and 4 formed on an arbitrary substrate 1, for example.Furthermore, the invention is not limited to two-stack type tandem-typestructure in which the two photoelectric conversion units 3 and 4 arestacked and may be applicable to a tandem-type structure in which threeor more photoelectric conversion units are stacked.

As an example of a method of manufacturing a tandem-type thin filmphotoelectric conversion device according to the embodiments in FIGS. 1and 2, a method of manufacturing a hybrid thin film solar cell having atwo-stack type super straight structure including the amorphous siliconunit 3 and the crystalline silicon unit 4 will be described below withreference to a reference example and comparative examples.

EXAMPLE 1

Example 1 corresponds to a method of manufacturing a thin film solarcell in FIG. 2. First of all, a transparent electrode layer 2 containingtin oxide as a main component was formed on a transparent glasssubstrate 1. Then, the laminate including the substrate 1 and theelectrode layer 2 was introduced in a first plasma CVD apparatus, and ap-type amorphous silicon carbide layer 31, an i-type amorphous siliconphotoelectric conversion layer 32 and an n-type microcrystalline siliconlayer 33 included in an amorphous silicon unit 3 were formed in thethickness of 8 nm, 300 nm and 10 nm, respectively, at a predeterminedsubstrate temperature. After the formation of the n-type layer 33,introduction of phosphine as doping gas was shut off in the samereaction chamber, and a non-doped intermediate layer 6 was formed in thethickness of 4 nm.

After that, the laminate was transferred to an unload chamber of thefirst plasma CVD apparatus, and the laminate was taken out to the airafter the camber was promptly filled with nitrogen gas. The laminate wasleft in the air for about 40 hours and then was introduced into a secondplasma CVD apparatus.

In the second plasma CVD apparatus, plasma exposure processing wascarried out at a predetermined substrate temperature for 20 seconds inan atmosphere in which hydrogen and phosphine gas were mixed. Theconcentration of the phosphine gas to hydrogen at that time was 200 ppm.Subsequently, silane gas was additionally introduced into the samechamber under substantially the same pressure condition while plasmadischarging by application of high frequency electric power wascontinued whereby an n-type microcrystalline silicon intermediate layer5 was deposited in the thickness of 20 nm in a mixed atmosphere ofsilane, hydrogen and phosphine.

After that, high frequency electric power was shut off once. Then, inthe same chamber under substantially the same pressure condition,introduction of phosphine gas was stopped and diborane gas wasintroduced into the chamber. Then, it was held for about 30 secondsuntil silane, hydrogen and diborane became stable as a mixed gasatmosphere. Then, high frequency power was applied thereto to causeplasma discharging to deposit a p-type microcrystalline silicon layer 41included in the crystalline silicon unit in the thickness of 16 nm.Table 1 shows detail conditions in the second plasma CVD apparatus forthe steps so far.

TABLE 1 Substrate Discharging Power Temperature Frequency DensityPressure Flow Rate (Relative Value) PH₃/H₂ (° C.) (MHZ) (W/cm²) (Pa)SiH₄ H₂ B₂H₆ PH₃ (ppm) Plasma 160 27.12 0.30 350 0 125 0 0.025 200Processing n-Type 160 27.12 0.30 350 1 125 0 0.025 — Layer 5 p-Type 16027.12 0.30 350 1 125 0.0025 0 — Layer 41

As is apparent from Table 1, plasma exposure processing in an atmosphereof a gas mixture containing phosphine and hydrogen, the formation of then-type intermediate layer 5 and the formation of the p-type layer 41were continuously carried out in the same chamber under the same setpressure. Furthermore, in Example 1, the discharging frequencies, theapplied power densities, the substrate temperatures and the gas flowrates were set uniformly, so that a series of processes and depositionsteps can be carried out quickly through simple manipulations ofopening/closing of valves of a gas introducing lines and turning on/offof plasma discharging.

A transient change may occur in the pressure in the chamber with theintroduction or shut-off of the doping gas or the semiconductor raw gas.However, the flow rates of these gases are lower than that of thecontinuously introduced hydrogen gas by about two orders or more ofmagnitude. Thus, the transient change in pressure can be significantlysmall. Therefore, the waiting time (time for stabilizing pressure and agas mixture ratio) before the deposition of the n-type intermediatelayer 5 and the p-type layer 41 can be as short as about 30 seconds intotal. In other words, the addition of the plasma exposure processingand the step of forming the n-type intermediate layer 5 hardly cause atime loss in the process for manufacturing a solar cell.

After the formation of the p-type layer 41, a non-doped i-typecrystalline silicon photoelectric conversion layer 42 and an n-typemicrocrystalline silicon layer 43 included in the crystalline siliconunit 4 were formed in the thickness of 1.7 μm and 15 nm, respectively,in the second plasma CVD apparatus. Then, the laminate was transferredto the unload chamber of the second plasma CVD apparatus, and thechamber was filled with nitrogen gas promptly. Then, the laminate wastaken out to the air.

Then, a zinc oxide film having a thickness of 30 nm, a silver filmhaving a thickness of 240 nm a titan film having a thickness of 5 nmincluded in a back electrode 10 were formed by sputtering. Through thesefilm forming steps, the two-stack type hybrid-type thin film solar cellas shown in FIG. 2 in which the amorphous silicon unit 3 and thecrystalline silicon unit 4 are stacked was formed.

By using a solar simulator, light of AM 1.5 spectrum was irradiated tothe hybrid thin film solar cell of Example 1 at energy density of 1kW/m² at 25 ° C., and the photoelectric conversion efficiency wasmeasured. Relative values of the result are shown in Table 2. ThoughTable 2 includes examples other than Example 1, maximum values, minimumvalues and mean values of photoelectric conversion efficiencies of 20samples (N=20) are shown for all cases. The values are standardized byreferring the mean value of Example 1 to be 100.

TABLE 2 Maximum Average Value at Value Minimum Value N = 20 Example 1101.4 97.4 100.0 Example 2 100.4 96.0 99.1 Reference Example 102.7 98.7101.0 Comparative 98.6 90.1 95.6 Example 1 Comparative 100.8 93.4 97.7Example 2 Example 3 101.1 96.6 99.3 Comparative 100.5 93.9 97.8 Example3 Example 4 101.3 96.5 99.5 Comparative 98.9 93.5 97.2 Example 4

EXAMPLE 2

Example 2 was different from Example 1 only in that the thickness of then-type microcrystalline silicon layer 33 in the amorphous silicon unit 3was increased from 10 nm to 12 nm, and thereafter the laminate was takenout from the first plasma CVD apparatus to the air without formation ofthe non-doped intermediate layer 6. In other words, Example 2corresponds to a method of manufacturing a hybrid thin film solar cellin FIG. 1.

REFERENCE EXAMPLE

Reference Example was different from Example 2 only in that thethickness of the n-type microcrystalline silicon layer 33 was increasedto 30 nm and the crystalline silicon unit 4 was subsequently formedwithout exposure of the laminate to the air and also without formationof the n-type intermediate layer 5.

As shown in Table 2, it is understood that the decreases in the averagephotoelectric conversion efficiency of the solar cells according to bothof Example 1 and Example 2 fall within the range of less than 2% incomparison with the solar cell according to Reference Example, which wasformed without exposure to the air, and the variations in conversionefficiency of the solar cells according to Example 1 and 2 are almostthe same as that of Reference Example. It is also understood thatExample 1 in which the non-doped intermediate layer 6 was formed has aslightly higher conversion efficiency than that of Example 2.

FIG. 3 is a transmission electron microscopic (TEM) photograph showing across section of a part in the vicinity of the boundary between theamorphous unit 3 and crystalline unit 4 in Example 1. The transparentelectrode 2 partially appears at the bottom of the photograph. When anoxide film or contaminated layer is formed on the non-doped intermediatelayer 6, which was exposed to the air, such a foreign substance layermay be clearly observed on a TEM photograph. However, on the TEMphotograph in FIG. 3, a clear foreign substance layer is not observedbetween the amorphous unit 3 and the crystalline unit 4. Only the changefrom the amorphous state to the crystalline state can be observed.

Similarly, FIG. 4 is a TEM photograph showing a cross section of a partin the vicinity of the boundary between the amorphous unit 3 and thecrystalline unit 4 in Reference Example. Since the laminate was notexposed to the air between the formation of the amorphous silicon unit 3and the crystalline unit 4 in Reference Example, no foreign substancelayer can be observed between the amorphous unit 3 and the crystallineunit 4 on the TEM photograph in FIG. 4 as a matter of course. Only thechange from the amorphous state to the crystalline state can beobserved.

From the similarity between the FIG. 3 and FIG. 4 as described above,even when the surface of the non-doped intermediate layer 6 was exposedto the air and thereby it was oxidized or contaminated in Example 1, theplasma exposure processing in the second plasma CVD apparatus mightremove and clean a foreign substance layer such as an oxidized film or acontamination film. In other words, the plasma exposure processing canprovide the same effect as that of the case in which the laminate wasnot exposed into the air between the formation step of the amorphousunit 3 and the formation step of the crystalline unit 4.

COMPARATIVE EXAMPLE 1

Comparative Example 1 was different from Example 1 only in that plasmaexposure processing on a surface of the laminate was omitted in thesecond plasma CVD apparatus.

COMPARATIVE EXAMPLE 2

Comparative Example 2 was different from Example 1 only in that plasmaexposure processing was carried out on a surface of the laminate in anatmosphere of hydrogen gas only in the second plasma CVD apparatus, andthen silane gas and phosphine gas were additionally introduced so thatthe n-type microcrystalline silicon intermediate layer 5 was formed.

According to Table 2, the average conversion efficiency in the case inwhich plasma exposure processing was not carried out as in ComparativeExample 1 is lower than that of Example 1 by 4% or above. On the otherhand, though the conversion efficiency improved slightly when plasmaexposure process with hydrogen only was carried out as in ComparativeExample 2, a large variation in the conversion efficiency was exhibited,and the average efficiency was apparently lower than that of Example 1.

EXAMPLE 3 AND COMPARATIVE EXAMPLE 3

Example 3 and Comparative Example 3 were different from Example 1 onlyin that the concentration of phosphine to hydrogen was 20 ppm (example3) and 4 ppm (Comparative Example 3), which are 1/10 and 1/50,respectively, of that of Example 1, in plasma exposure processingcarried out on the surface of the laminate in the mixed atmosphere ofphosphine and hydrogen. From Table 2, the conversion efficiency ofComparative Example 3 in which 4 ppm phosphine was added at plasmaexposure processing is not much different from that of ComparativeExample 2 in which no phosphine was added. However, the conversionefficiency of Example 3 in which 20 ppm phosphine was added exhibitsthat the phosphine in the concentration is sufficiently effective.

EXAMPLE 4 AND COMPARATIVE EXAMPLE 4

Example 4 and Comparative Example 4 were different from Example 1 onlyin that the processing time of plasma exposure processing carried out ona surface of the laminate in an atmosphere of a gas mixture of phosphineand hydrogen gas was 60 seconds (Example 4) and 180 seconds (ComparativeExample 4), which are 3 times and 9 times, respectively, of those ofExample 1. From Table 2, the effects are not much different even whenthe plasma exposure processing time is increased from 20 seconds inExample 1 to 60 seconds in Example 4. However, the conversion efficiencyadversely decreases when the processing time was extended to 180 secondsin Comparative example 4.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, when thesubstrate having one or more units is once taken out from the depositionapparatus to the air in mid-course of the formation of the plurality ofphotoelectric conversion units included in the tandem-type thin filmphotoelectric conversion device, the reduction in photoelectricconversion efficiency of the completed apparatus due to the air exposurecan be minimized. Thus, the photoelectric conversion units can be formeddiscontinuously by using separate deposition apparatuses, and theflexibility and production efficiency of steps of manufacturing atandem-type thin film photoelectric conversion device can be improved.

1. A method of manufacturing a tandem-type thin film photoelectricconversion device comprising the steps of: forming at least onephotoelectric conversion unit through sequentially stacking a firstone-conductivity type layer, a first photoelectric conversion layer ofsubstantially intrinsic semiconductor and a first opposite-conductivitytype layer on a substrate in a deposition apparatus; taking out thesubstrate having the photoelectric conversion unit from the depositionapparatus to air, wherein a non-doped intermediate layer having athickness of 5 nm or less is formed subsequently to the step of formingthe at least one photoelectric conversion unit on the substrate and thenthe substrate is taken out to the air; introducing the substrate into adeposition apparatus and carrying out plasma exposure processing on thesubstrate in an atmosphere of a gas mixture containing an impurityelement for determining the conductivity type of the same conductivitytype as that of the first opposite-conductivity type layer and hydrogen;forming a conductivity type intermediate layer by additionally supplyingsemiconductor raw gas to the deposition apparatus; and then forming asubsequent photoelectric conversion unit through sequentially stacking asecond one-conductivity type layer, a second photoelectric conversionlayer of substantially intrinsic semiconductor and a secondopposite-conductivity type layer.
 2. A method of manufacturing atandem-type thin film photoelectric conversion device according to claim1, characterized in that the tandem-type thin film photoelectricconversion device includes at least one amorphous silicon thin filmphotoelectric conversion unit and at least one crystalline silicon thinfilm photoelectric conversion unit.
 3. A method of manufacturing atandem-type thin film photoelectric conversion device according to claim1, characterized in that the plasma exposure processing and theformation of the conductivity-type intermediate layer are carried out inthe same deposition apparatus.
 4. A method of manufacturing atandem-type thin film photoelectric conversion device according to claim1, characterized in that the plasma exposure processing and theformation of the conductivity-type intermediate layer are carried outunder substantially the same pressure.